man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

utmpname(3C)

Name

getutent, getutid, getutline, pututline, setutent, endutent, utmpname - user accounting database functions

Synopsis

#include <utmp.h>

struct utmp *getutent(void);
struct utmp *getutid(const struct utmp *id);
struct utmp *getutline(const struct utmp *line);
struct utmp *pututline(const struct utmp *utmp);
void setutent(void);
void endutent(void);
int utmpname(const char *file);

Description

These functions provide access to the user accounting database, utmp. Entries in the database are described by the definitions and data structures in <utmp.h>.

The utmp structure contains the following members:

char                ut_user[8];   /* user login name */
char                ut_id[4];     /* /etc/inittab id */
                                  /* (usually line #) */
char                ut_line[12];  /* device name (console, lnxx) */
short               ut_pid;       /* process id */
short               ut_type;      /* type of entry */
struct exit_status  ut_exit;      /* exit status of a process */
                                  /* marked as DEAD_PROCESS */
time_t              ut_time;      /* time entry was made */

The structure exit_status includes the following members:

short   e_termination;   /* termination status */
short   e_exit;          /* exit status */

getutent()

The getutent() function reads in the next entry from a utmp database. If the database is not already open, it opens it. If it reaches the end of the database, it fails.

getutid()

The getutid() function searches forward from the current point in the utmp database until it finds an entry with a ut_type matching id->ut_type if the type specified is RUN_LVL, BOOT_TIME, DOWN_TIME, OLD_TIME, or NEW_TIME. If the type specified in id is INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS, then getutid() will return a pointer to the first entry whose type is one of these four and whose ut_id member matches id->ut_id. If the end of database is reached without a match, it fails.

getutline()

The getutline() function searches forward from the current point in the utmp database until it finds an entry of the type LOGIN_PROCESS or ut_line string matching the line->ut_line string. If the end of database is reached without a match, it fails.

pututline()

The pututline() function writes the supplied utmp structure into the utmp database. It uses getutid() to search forward for the proper place if it finds that it is not already at the proper place. It is expected that normally the user of pututline() will have searched for the proper entry using one of the these functions. If so, pututline() will not search. If pututline() does not find a matching slot for the new entry, it will add a new entry to the end of the database. It returns a pointer to the utmp structure. When called by a non-root user, pututline() invokes a setuid() root program to verify and write the entry, since the utmp database is normally writable only by root. In this event, the ut_name member must correspond to the actual user name associated with the process; the ut_type member must be either USER_PROCESS or DEAD_PROCESS; and the ut_line member must be a device special file and be writable by the user.

setutent()

The setutent() function resets the input stream to the beginning. This reset should be done before each search for a new entry if it is desired that the entire database be examined.

endutent()

The endutent() function closes the currently open database.

utmpname()

The utmpname() function allows the user to change the name of the database file examined to another file. If the file does not exist, this will not be apparent until the first attempt to reference the file is made. The utmpname() function does not open the file but closes the old file if it is currently open and saves the new file name.

Return Values

A null pointer is returned upon failure to read, whether for permissions or having reached the end of file, or upon failure to write. If the file name given is longer than 79 characters, utmpname() returns 0. Otherwise, it returns 1.

Usage

These functions use buffered standard I/O for input, but pututline() uses an unbuffered non-standard write to avoid race conditions between processes trying to modify the utmp and wtmp databases.

Applications should not access the utmp and wtmp databases directly, but should use these functions to ensure that these databases are maintained consistently. Using these functions, however, may cause applications to fail if user accounting data cannot be represented properly in the utmp structure (for example, on a system where PIDs can exceed 32767). Use the functions described on the getutxent(3C) manual page instead.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
MT-Level
Unsafe

See Also

getutxent(3C), ttyslot(3C), utmpx(4), attributes(5)

Notes

The most current entry is saved in a static structure. Multiple accesses require that it be copied before further accesses are made. On each call to either getutid() or getutline(), the function examines the static structure before performing more I/O. If the contents of the static structure match what it is searching for, it looks no further. For this reason, to use getutline() to search for multiple occurrences, it would be necessary to zero out the static area after each success, or getutline() would just return the same structure over and over again. There is one exception to the rule about emptying the structure before further reads are done. The implicit read done by pututline() (if it finds that it is not already at the correct place in the file) will not hurt the contents of the static structure returned by the getutent(), getutid() or getutline() functions, if the user has just modified those contents and passed the pointer back to pututline().